Prevent an exclusivity benchmark from being optimized too much.

Author: atrick

benchmark/single-source/Exclusivity.swift

@@ -80,7 +80,7 @@ public func run_accessGlobal(_ N: Int) {
 // Hopefully the optimizer will not see this as "final" and optimize away the
 // materializeForSet.
 public class C {
-  var counter = 0
+  public var counter = 0
 
   func inc() {
     counter += 1